I have such a unit in my '72. Is this a 2 channel unit? The speaker wire harness coming out of the radio is a female 3 pronged with male spades, and I would like to run 2 sets of 4 ohm speakers. If the radio is a 2 channel, then how is this accomplished? The three prong is pos right, pos left, and ? (negative both). If the radio is 2 channel, how does this get separated, for the purposes of not having too much impedance for the unit? Thanks I have read tons of posts on the forum about this stuff and it's all getting cloudier as I re read some of it. I will rewire each side in series with 4 ohm probably 30 - 50 watt speakers if I have 2 channels. Thanks. Lots of those posts had info from 71Tvette, hope to hear from him.

 

I just asked this question when I purchased new dash speakers from turnswitch. I was told if I had decided to use my existing speakers with the original radio I would need to series the newer speakers to get to the proper impedance. i will check my notes on the range he told me to try to stay in and update.

 

Some units were mono and some stero....You need to figure out which unit you have first and then make sure you have the correct amp (it's not an amp but looks like one) the correct one for stero has 2 transistors while the mono unit only has one.

Brian

 

Mine is a mono system "70" and I have the same plug , I think you are correct 2 positives and 1 ground . But not sure on the ohm's . I think on the upper slide it should say FM Stereo, mine does not.

 

My notes just say to check with multimeter across speaker terminals 10 ohm will test read 6.8-7.2 on meter (parallel these)
4 ohm speakers will read 2.3 on multimeter series these

This is what the 2 transistor convector looks like
And you can identify the stereo units by the white sot to the right of the FM on the am/fm selector

 

As my title implied, it is a stereo unit, here are pictures of the radio, convector underside and pigtail during bench testing/operation.

 

Thank you for posting I realize I need mounting brackets for my convector. Yours looks to be in excellent condition good luck with the install

 

I asked similar questions a few months ago on this forum and got a lot of good information from 2 posters. You may want to search back to that post. Here are the conclusions I came to: First, the center terminal is the common. Second the 4 ohm speakers have to be wired in series. Third, use the same speakers in all 4 locations. Fourth, it is a two channel and you can't bias the volume between the speakers on the same channel.
Not sure about the impedance but you are replacing a 10 ohm speaker with 2 four ohm speakers in series so I think you can overload the circuit. That being said, I will never operate the radio at full volume so this is not an issue for me.

My criteria with the speakers was that they fit in the dash. This radio is old technology and I am not an audiophile, so I don't think or even care if I ever get great sound from it. Reasonably good speakers are more than adequate for me as long as they fit. Even after extensive searching and buying the speakers that were supposed to fit, they didn't. The cone hit the X brace in the mounting bracket. I shimmed the space between the speaker and the bracket with 1/8" thick gasket material.
I just went through this and I feel your pain. If you need any other information I'll tell you what I did and why.

 

I agree with 2manyvets. I think your limiting factor will be I think the oe stereo is a 6 watt setup or something like that. With too many speakers you will not have the power to drive them. Like him I decided to just install 2 new oe dash speakers. I am not a Radiohead either this is just the conclusion I came to from my research and discussion with turnswitch.

 

So as for this issue, I am grateful to everyone for their assistance. I had not used the 3 pronged pigtail properly when I first hooked up the stereo many years ago. I was ignoring the ground/common altogether, robbing myself of any stereo sound I could have be hearing, such as it is. So I will be installing 2 new dash speakers and properly wiring for 2 in the back. I will be wiring the front in a series and the back in a series so that I will be able to fade the sound front/back and will be bench testing this prior to installation. Be glad when it is finished.